The transcutaneous electrical stimulation (TES) treatment for controlling pain involves the application of periodic electrical pulses to the skin of the patient in the painful region. The equipment presently in use applies the pulses via skin electrodes coupled to a pulse generator which generates symmetrical (e.g. sine wave, square-wave, bell-shaped or triangular) pulses of fixed frequency and width. This treatment has been found effective to reduce pain in many (but not all) cases, and many theories have been proposed attempting to explain the mechanism of action by which it accomplishes this.